A system for quickly accessing user permissions in an access control list includes a first cache memory (2), a second cache memory (3), a permission querying module (12), a permission merging module (13), and an information unit generating module (14). The first cache memory is for storing a plurality of first information units (20). The second cache memory is for storing a plurality of second information units (30). The permission querying module is for querying the user permissions stored in the first cache memory and the second cache memory, and respectively storing first information units and second information units in the first cache memory and the second cache memory. The permission merging module is for merging different user permissions. The information unit generating module is for generating the first information units and the second information units. A related method is also disclosed.